Aromatic Isomerization Catalyst and Isomerization Process

ABSTRACT

One exemplary embodiment can be an extruded C8 alkylaromatic isomerization catalyst. The extruded catalyst can include:
         about 2-about 20%, by weight, of an MTW zeolite;   about 80-about 98%, by weight, of a binder including an alumina;   about 0.01-about 2.00%, by weight, of a noble group metal calculated on an elemental basis; and   about 100 ppm-less than about 1000 ppm, by weight, of at least one alkali metal calculated on an elemental basis.
 
Generally, the weight percents of the MTW zeolite, the binder, the noble group metal, and the at least one alkali metal are based on a weight of the extruded catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of pending U.S. application Ser. No.11/965,925, filed Dec. 28, 2007, which is a Continuation-In-Part ofpending U.S. application Ser. No. 11/868,844, filed Oct. 8, 2007. U.S.application Ser. Nos. 11/965,925 and 11/868,844 are hereby incorporatedby reference in their entirety.

FIELD OF THE INVENTION

The field of this invention generally relates to a catalyst for a C8aromatic isomerization process or zone, and/or an isomerization process.

BACKGROUND OF THE INVENTION

The xylenes, such as para-xylene, meta-xylene and ortho-xylene, can beimportant intermediates that find wide and varied application inchemical syntheses. Generally, para-xylene upon oxidation yieldsterephthalic acid that is used in the manufacture of synthetic textilefibers and resins. Meta-xylene can be used in the manufacture ofplasticizers, azo dyes, wood preservers, etc. Generally, ortho-xylene isfeedstock for phthalic anhydride production.

Xylene isomers from catalytic reforming or other sources generally donot match demand proportions as chemical intermediates, and furthercomprise ethylbenzene, which can be difficult to separate or to convert.Typically, para-xylene is a major chemical intermediate with significantdemand, but amounts to only 20-25% of a typical C8 aromatic stream.Adjustment of an isomer ratio to demand can be effected by combiningxylene-isomer recovery, such as adsorption for para-xylene recovery,with isomerization to yield an additional quantity of the desiredisomer. Typically, isomerization converts a non-equilibrium mixture ofthe xylene isomers that is lean in the desired xylene isomer to amixture approaching equilibrium concentrations.

Various catalysts and processes have been developed to effect xyleneisomerization. In selecting an appropriate technology, it is desirableto run the isomerization process as close to equilibrium as practical inorder to maximize the para-xylene yield; however, associated with thisis a greater cyclic C8 loss due to side reactions. Often, the approachto equilibrium that is used is an optimized compromise between high C8cyclic loss at high conversion (i.e., very close approach toequilibrium) and high utility costs due to the large recycle rate ofunconverted C8 aromatic. Thus, catalysts can be evaluated on the basisof a favorable balance of activity, selectivity and stability.

Catalysts can be made by several different processes. Generally,producing an extruded catalyst that can isomerize ethylbenzene toxylenes while minimizing C8 ring loss would be beneficial.

BRIEF SUMMARY OF THE INVENTION

One exemplary embodiment can be an extruded C8 alkylaromaticisomerization catalyst. The extruded catalyst can include:

-   -   about 2-about 20%, by weight, of an MTW zeolite;    -   about 80-about 98%, by weight, of a binder including an alumina;    -   about 0.01-about 2.00%, by weight, of a noble group metal        calculated on an elemental basis; and    -   about 100 ppm-less than about 1000 ppm, by weight, of at least        one alkali metal calculated on an elemental basis.        Generally, the weight percents of the MTW zeolite, the binder,        the noble group metal, and the at least one alkali metal are        based on a weight of the extruded catalyst.

Another exemplary embodiment can be an extruded C8 alkylaromaticisomerization catalyst. The extruded catalyst can include:

-   -   about 2-about 20%, by weight, of an MTW zeolite where the MTW        zeolite may include about 4,000-about 8,000 ppm, by weight, of        at least one alkali metal calculated on an elemental basis based        on the weight of the zeolite;    -   about 80-about 98%, by weight, of a binder including an alumina;        and    -   about 0.01-about 2.00%, by weight, of a noble group metal        calculated on an elemental basis.        Generally, the weight percents of the MTW zeolite, the binder,        and the noble group metal are based on a weight of the extruded        catalyst.

A further exemplary embodiment is a process for isomerizing anon-equilibrium C8 aromatic feed to provide an isomerized product. Theprocess can include contacting the non-equilibrium C8 aromatic feed withan extruded C8 alkylaromatic isomerization catalyst, and providing theisomerized product having a C8 ring loss of no more than about 2.5.Typically, the extruded catalyst includes:

-   -   about 2-about 20%, by weight, of an MTW zeolite;    -   about 80-about 98%, by weight, of a binder including an alumina;    -   about 0.01-about 2.00%, by weight, of a noble group metal        calculated on an elemental basis; and    -   about 100 ppm-less than about 1000 ppm, by weight, of at least        one alkali metal calculated on an elemental basis.        Generally, the weight percents of the MTW zeolite, the binder,        the noble group metal, and at least one alkali metal are based        on a weight of the extruded catalyst.

Therefore, the catalyst can provide lower C8 ring losses. In someexemplary embodiments, a catalyst with a higher alkali metal content by,e.g., omitting a catalyst wash, can yield a catalyst with a low C8 ringloss.

DEFINITIONS

As used herein, the term “zone” can refer to an area including one ormore equipment items and/or one or more sub-zones. Equipment items caninclude one or more reactors or reactor vessels, heaters, separators,exchangers, pipes, pumps, compressors, and controllers. Additionally, anequipment item, such as a reactor or vessel, can further include one ormore zones or sub-zones.

As used herein, the term “stream” can be a stream including varioushydrocarbon molecules, such as straight-chain, branched, or cyclicalkanes, alkenes, alkadienes, and alkynes, and optionally othersubstances, such as gases, e.g., hydrogen, or impurities, such as heavymetals. The stream can also include aromatic and non-aromatichydrocarbons. Moreover, the hydrocarbon molecules may be abbreviated C1,C2, C3 . . . Cn where “n” represents the number of carbon atoms in thehydrocarbon molecule.

As used herein, the term “aromatic” can mean a group containing one ormore rings of unsaturated cyclic carbon radicals where one or more ofthe carbon radicals can be replaced by one or more non-carbon radicals.An exemplary aromatic compound is benzene having a C6 ring containingthree double bonds. Other exemplary aromatic compounds can includepara-xylene, ortho-xylene, meta-xylene and ethylbenzene. Moreover,characterizing a stream or zone as “aromatic” can imply one or moredifferent aromatic compounds.

As used herein, the term “support” generally means a molecular sievethat has been combined with a binder before the addition of one or moreadditional catalytically active components, such as a noble metal, or asubsequent process such as reducing or sulfiding.

DETAILED DESCRIPTION OF THE INVENTION

Generally, a refinery or a petrochemical production facility can includean aromatic production facility or an aromatic complex, particularly aC8 aromatic complex that purifies a reformate to extract one or morexylene isomers, such as para-xylene or meta-xylene. Such an aromaticcomplex for extracting para-xylene is disclosed in U.S. Pat. No.6,740,788 B1. A feedstock to an aromatic complex can include anisomerizable aromatic hydrocarbon of the general formulaC₆H(_(6-n))R_(n), where n is an integer from 2 to 5 and R is CH₃, C₂H₅,C₃H₇, or C₄H₉, in any combination and including all the isomers thereof.Suitable aromatic hydrocarbons may include ortho-xylene, meta-xylene,para-xylene, ethylbenzene, ethyltoluene, tri-methylbenzene,di-ethylbenzene, tri-ethylbenzene, methylpropylbenzene,ethylpropylbenzene, di-isopropylbenzene, or a mixture thereof.

An aromatic complex can include a xylene isomer separation zone, such asa para-xylene separation zone, and a C8 aromatic isomerization zone. TheC8 aromatic isomerization zone can receive a stream depleted of at leastone xylene isomer, such as para-xylene or meta-xylene. The C8 aromaticisomerization zone can reestablish the equilibrium concentration ofxylene isomers and convert other compounds, such as ethylbenzene, into axylene. Typically, such a zone can increase the amount of a xyleneisomer, such as para-xylene, and the product from that C8 aromaticisomerization zone can be recycled to the xylene isomer separation zoneto recover more of the desired isomer.

One exemplary application of the catalyst disclosed herein is theisomerization of a C8 aromatic mixture containing ethylbenzene andxylenes. Generally, the mixture has an ethylbenzene content of about1-about 50%, by weight, an ortho-xylene content of up to about 35%, byweight, a meta-xylene content of about 20-about 95%, by weight, and apara-xylene content of up to about 30%, by weight. The aforementioned C8aromatics are a non-equilibrium mixture, i.e., at least one C8 aromaticisomer is present in a concentration that differs substantially from theequilibrium concentration at isomerization conditions. Usually thenon-equilibrium mixture is prepared by removal of para-, ortho- and/ormeta-xylene from a fresh C8 aromatic mixture obtained from an aromaticproduction process.

Accordingly, a C8 aromatic hydrocarbon feed mixture, preferably inadmixture with hydrogen, can be contacted with a catalyst hereinafterdescribed in an C8 aromatic hydrocarbon isomerization zone. Contactingmay be effected using the catalyst in a fixed bed system, a moving bedsystem, a fluidized bed system, or in a batch operation. Preferably, afixed bed system is utilized. In this system, a hydrogen-rich gas andthe feed mixture are preheated by any suitable heating means to thedesired reaction temperature and then passed into a C8 aromaticisomerization zone containing a fixed bed of catalyst. The conversionzone may be one or more separate reactors with suitable meanstherebetween to ensure that the desired isomerization temperature ismaintained at the entrance of each zone. The reactants may be contactedwith the catalyst bed in either upward-, downward-, or radial-flowfashion, and the reactants may be in the liquid phase, a mixedliquid-vapor phase, or a vapor phase when contacted with the catalyst.

The feed mixture, preferably a non-equilibrium mixture of C8 aromatics,may be contacted with the isomerization catalyst at suitable C8isomerization conditions. Generally, such conditions include atemperature ranging from about 0-about 600° C. or more, preferably about300-about 500° C. Generally, the pressure is from about 100-about 10,000kPa absolute, preferably less than about 5,000 kPa. Sufficient catalystmay be contained in the isomerization zone to provide a liquid hourlyspace velocity with respect to the hydrocarbon feed mixture of fromabout 0.1-about 30 hr⁻¹, and preferably about 0.5-about 10 hr⁻¹. Thehydrocarbon feed mixture can be reacted in admixture with hydrogen at ahydrogen/hydrocarbon mole ratio of about 0.5:1-about 25:1 or more. Otherinert diluents such as nitrogen, argon and light hydrocarbons may bepresent.

The reaction can isomerize xylenes while reacting ethylbenzene to form axylene mixture via conversion to and reconversion from naphthenes. Thus,the yield of xylenes in the product may be enhanced by forming xylenesfrom ethylbenzene. Typically, the loss of C8 aromatics through thereaction is low, generally less than about 4%, by mole, preferably nomore than about 3.5%, by mole, and most preferably less than about 3%,by mole, per pass of C8 aromatics in the feed to the reactor.

Any effective recovery scheme may be used to recover an isomerizedproduct from the effluent of the reactors. Typically, the liquid productis fractionated to remove light and/or heavy byproducts to obtain theisomerized product. Heavy byproducts can include aromatic C10 compoundssuch as dimethylethylbenzene. In some instances, certain product speciessuch as ortho-xylene or dimethylethylbenzene may be recovered from theisomerized product by selective fractionation. The product fromisomerization of C8 aromatics usually is processed to selectivelyrecover the para-xylene isomer, optionally by crystallization. Selectiveadsorption can be accomplished by using crystalline aluminosilicatesaccording to U.S. Pat. No. 3,201,491.

A catalyst of the C8 aromatic isomerization zone can include at leastone MTW zeolitic molecular sieve, also characterized as “low silicaZSM-12” and can include molecular sieves with a silica to alumina ratioless than about 45, preferably from about 20-about 40. Preferably, theMTW zeolite is substantially mordenite-free, which generally means anMTW component containing less than about 20%, by weight, mordeniteimpurity, preferably less than about 10%, by weight, and most preferablyless than about 5%, by weight, mordenite.

The preparation of an MTW zeolite by crystallizing a mixture includingan alumina source, a silica source and a templating agent is known. U.S.Pat. No. 3,832,449 discloses an MTW zeolite using tetraalkylammoniumcations. U.S. Pat. No. 4,452,769 and U.S. Pat. No. 4,537,758 disclose amethyltriethylammonium cation to prepare a highly siliceous MTW zeolite.U.S. Pat. No. 6,652,832 uses an N,N-dimethylhexamethyleneimine cation asa template to produce low silica-to-alumina ratio MTW zeolite withoutMFI impurities. Preferably high purity crystals are used as seeds forsubsequent batches.

The MTW zeolite is preferably composited with a binder for convenientformation of particles. The proportion of zeolite in the catalyst isabout 1-about 90%, by weight, preferably about 2-about 20%, by weight,and optimally about 5-about 10%, by weight. Generally, it is desirablefor the MTW zeolite to contain about 0.3-about 0.5%, by weight, Na₂O andabout 0.3-about 0.5%, by weight, K₂O. On an elemental basis, the MTWzeolite can contain about 4,000-8,000 ppm, by weight, of at least onealkali metal, preferably sodium and/or potassium. Typically, the MTWzeolite can contain about 2,000-about 4,000 ppm, by weight, sodium andabout 2,000-about 4,000 ppm, by weight, potassium calculated on anelemental basis. Also, in one exemplary embodiment it is desirable forthe molar ratio of silica to alumina to be about 36:1 and the molarratio of (Na+K)/Al to be about 0.2-about 0.3.

Generally, the zeolite is combined with a refractory inorganic oxidebinder. The binder should be a porous, adsorptive support having asurface area of about 25-about 500 m²/g, preferably about 200-about 500m²/g. Desirably, the inorganic oxide is an alumina, such as agamma-alumina. Such a gamma-alumina can be derived from a boehmite or apseudoboehmite alumina (hereinafter collectively may be referred to as“boehmite alumina”). The boehmite alumina can be compounded with thezeolite and extruded. During oxidation (or calcination), the boehmitealumina may be converted into gamma-alumina. One desired boehmitealumina utilized as a starting material is VERSAL-251 sold by UOP, LLCof Des Plaines, Ill. Another boehmite alumina can be sold under thetrade designation CATAPAL C by Sasol North America of Houston, Tex.Generally, the catalyst can have about 10-about 99%, by weight,desirably about 90-about 99%, by weight, of the gamma-alumina binder.Similarly, the catalyst can include about 80-about 98%, by weight,preferably about 90-about 95%, by weight, of an alumina binder.

The alumina binder can have up to about 100 ppm sodium, up to about 200ppm calcium, and up to about 200 ppm magnesium, by weight, calculated onan elemental basis based on the weight of the binder. Generally, theVERSAL-251 alumina can have up to about 100 ppm sodium, up to about 200ppm calcium, and up to about 200 ppm magnesium, by weight, calculated onan elemental basis based on the weight of the binder. Typically, theCATAPAL C alumina can have up to about 30 ppm sodium, up to about 50 ppmcalcium, and up to about 20 ppm magnesium, by weight, calculated on anelemental basis based on the weight of the binder.

One shape for the support or catalyst can be an extrudate. Generally,the extrusion initially involves mixing of the molecular sieve withoptionally the binder and a suitable peptizing agent to form ahomogeneous dough or thick paste having the correct moisture content toallow for the formation of extrudates with acceptable integrity towithstand direct calcination. Extrudability may be determined from ananalysis of the moisture content of the dough, with a moisture contentin the range of from about 30-about 70%, by weight, being preferred. Thedough may then be extruded through a die pierced with multiple holes andthe spaghetti-shaped extrudate can be cut to form particles inaccordance with known techniques. A multitude of different extrudateshapes is possible, including a cylinder, cloverleaf, dumbbell, andsymmetrical and asymmetrical polylobates. Furthermore, the dough orextrudates may be shaped to any desired form, such as a sphere, by,e.g., marumerization that can entail one or more moving plates orcompressing the dough or extrudate into molds.

Alternatively, support or catalyst pellets can be formed into sphericalparticles by accretion methods. Such a method can entail adding liquidto a powder mixture of zeolite and binder in a rotating pan or conicalvessel having a rotating auger.

Generally, preparation of alumina-bound spheres involves dropping amixture of molecular sieve, alsol, and gelling agent into an oil bathmaintained at elevated temperatures. Examples of gelling agents that maybe used in this process include hexamethylene tetraamine, urea, andmixtures thereof. The gelling agents can release ammonia at the elevatedtemperatures which sets or converts the hydrosol spheres into hydrogelspheres. The spheres may then be withdrawn from the oil bath andtypically subjected to specific aging treatments in oil and an ammoniasolution to further improve their physical characteristics. Oneexemplary oil dropping method is disclosed in U.S. Pat. No. 2,620,314.

Generally, the subsequent drying, calcining, and optional washing stepscan be done before and/or after impregnation with one or morecomponents, such as metal. Preferably after formation of the binder andzeolite into a support, the support can be dried at a temperature ofabout 50-about 320° C., preferably about 100-about 200° C. for a periodof about 1-about 24 hours or more. Next, the support is usually calcinedor oxidized at a temperature of 50-about 700° C., desirably about540-about 650° C. for a period of about 1-about 20 hours, desirablyabout 1-about 1.5 hours in an air atmosphere until the metalliccompounds, if present, are converted substantially to the oxide form,and substantially all the alumina binder is converted to gamma-alumina.If desired, the optional halogen component may be adjusted by includinga halogen or halogen-containing compound in the air atmosphere. Thevarious heat treating steps may be conducted multiple times such asbefore and after addition of components, such as one or more metals, tothe support via impregnation as is well known in the art. Steam may bepresent in the heat treating atmospheres during these steps. Duringcalcination and/or other heat treatments to the catalyst, the pore sizedistribution of the alumina binder can be shifted to larger diameterpores. Thus, calcining the catalyst can increase the average pore sizeof the catalyst.

Optionally, the catalyst can be washed. Typically, the catalyst can bewashed with a solution of ammonium nitrate or ammonium hydroxide,preferably ammonium hydroxide. Generally, the wash is conducted at atemperature of about 50-about 150° C. for about 1-about 10 hours. In onedesired embodiment, no wash is conducted to provide an elevated level ofat least one alkali metal. Generally, a wash of ammonium nitrate canlower the amount of alkali metal in the catalyst, particularly thezeolite. Exemplary catalysts without a wash are depicted in US Pub. No.2005/0143615 A1. Preferably, no wash or a wash of ammonium hydroxide isconducted to allow much of the existing alkali metal to remain on thecatalyst. It should be understood, however, if the zeolite and/orbinder, particularly the zeolite, has an elevated alkali metal contentthen an ammonium nitrate wash can be conducted that allows some alkalimetal at a desired level to remain on the zeolite and/or binder.

In some exemplary embodiments, after drying, calcining, and optionallywashing, one or more components can be impregnated on the support. Thecatalyst may also include a noble metal, including one or more ofplatinum, palladium, rhodium, ruthenium, osmium, and iridium. Thepreferred noble metal is platinum. The noble metal component may existwithin the final catalyst as a compound such as an oxide, sulfide,halide, or oxysulfide, or as an elemental metal or in combination withone or more other ingredients of the catalyst. Desirably, the noblemetal component exists in a reduced state. This component may be presentin the final catalyst in any amount which is catalytically effective.Generally, the final catalyst includes about 0.01-about 2%, desirablyabout 0.05-about 1%, and optimally about 0.25-about 0.5%, by weight,calculated on an elemental basis of the noble metal, preferablyplatinum.

The noble metal component may be incorporated into the catalyst in anysuitable manner. One method of preparing the catalyst involves theutilization of a water-soluble, decomposable compound of a noble metalto impregnate the calcined sieve-binder composite. Alternatively, anoble metal compound may be added at the time of compositing the sievecomponent and binder. Complexes of noble metals that may be employed inimpregnating solutions, co-extruded with the sieve and binder, or addedby other known methods can include chloroplatinic acid, chloropalladicacid, ammonium chloroplatinate, bromoplatinic acid, platinumtrichloride, platinum tetrachloride hydrate, platinum dichlorocarbonyldichloride, tetramine platinic chloride, dinitrodiaminoplatinum, sodiumtetranitroplatinate (II), palladium chloride, palladium nitrate,palladium sulfate, diaminepalladium (II) hydroxide, andtetraminepalladium (II) chloride.

A Group IVA (IUPAC 14) metal component may also be incorporated into thecatalyst. Of the Group IVA (IUPAC 14) metals, germanium and tin arepreferred and tin is especially preferred. This component may be presentas an elemental metal, as a chemical compound such as the oxide,sulfide, halide, or oxychloride, or as a physical or chemicalcombination with the porous carrier material and/or other components ofthe catalyst. Preferably, a substantial portion of the Group IVA (IUPAC14) metal exists in the finished catalyst in an oxidation state abovethat of the elemental metal. The Group IVA (IUPAC 14) metal componentoptimally is utilized in an amount sufficient to result in a finalcatalyst containing about 0.01-about 5%, by weight, preferably about 0.1to about 2%, by weight, and optimally about 0.3-about 0.45, by weight,metal calculated on an elemental basis.

The Group IVA (IUPAC 14) metal component may be incorporated in thecatalyst in any suitable manner to achieve a homogeneous dispersion,such as by co-precipitation with the porous carrier material,ion-exchange with the carrier material or impregnation of the carriermaterial at any stage in the preparation. One method of incorporatingthe Group IVA (IUPAC 14) metal component into the catalyst involves theutilization of a soluble, decomposable compound of a Group IVA (IUPAC14) metal to impregnate and disperse the metal throughout the porouscarrier material. The Group IVA (IUPAC 14) metal component can beimpregnated either prior to, simultaneously with, or after the othercomponents are added to the carrier material. Thus, the Group IVA (IUPAC14) metal component may be added to the carrier material by comminglingthe latter with an aqueous solution of a suitable metal salt or solublecompound such as stannous bromide, stannous chloride, stannic chloride,stannic chloride pentahydrate; germanium oxide, germanium tetraethoxide,or germanium tetrachloride; or lead nitrate, lead acetate, or leadchlorate. The utilization of Group IVA (IUPAC 14) metal chloridecompounds, such as stannic chloride, germanium tetrachloride or leadchlorate, is particularly preferred since they can facilitate theincorporation of both the metal component and at least a minor amount ofthe preferred halogen component in a single step. When combined withhydrogen chloride during the especially preferred alumina peptizationstep as described above, a homogeneous dispersion of the Group IVA(IUPAC 14) metal component can be obtained. In an alternativeembodiment, organic metal compounds such as trimethyltin chloride anddimethyltin dichloride are incorporated into the catalyst during thepeptization of the alumina with hydrogen chloride or nitric acid.

The catalyst may also contain other metal components as well. Such metalmodifiers may include rhenium, cobalt, nickel, indium, gallium, zinc,uranium, dysprosium, thallium, or a mixture thereof. Generally, acatalytically effective amount of such a metal modifier may beincorporated into a catalyst to effect a homogeneous or stratifieddistribution.

The catalyst can also contain a halogen component, such as fluorine,chlorine, bromine, iodine or a mixture thereof, with chlorine beingpreferred. Desirably, the catalyst contains no added halogen other thanthat associated with other catalyst components.

The catalyst may also contain at least one alkali metal with a totalalkali metal content of the catalyst of at least about 100 ppm, byweight, calculated on an elemental basis. The alkali metal can belithium, sodium, potassium, rubidium, cesium, francium, or a combinationthereof. Preferred alkali metals can include sodium and potassium.Desirably, the catalyst contains no added alkali metal other than thatassociated with the zeolite and/or binder. Generally, the total alkalimetal content of the catalyst is at least about 200 ppm, desirably 300ppm, by weight, calculated on an elemental basis. Generally, the totalalkali metal content of the catalyst is no more than about 2500 ppm,desirably 2000 ppm, and optimally 1000 ppm, by weight, calculated on anelemental basis. In one preferred embodiment, the catalyst can haveabout 300 ppm-about 2500 ppm, by weight, of at least one alkali metalcalculated on an elemental basis. In a further embodiment, the catalystcan have about 100 ppm-less than about 1000 ppm, preferably about300-less than about 1000 ppm, and optimally about 300-about 700 ppm, byweight, of at least one alkali metal, preferably sodium and/orpotassium, calculated on an elemental basis. In yet another preferredembodiment, the catalyst can have at least about 150 ppm, preferablyabout 150-about 310 ppm, by weight, sodium and at least about 50 ppm,and preferably about 50-about 250 ppm, by weight, potassium, calculatedon an elemental basis.

The resultant catalyst can subsequently be subjected to a substantiallywater-free reduction step to ensure a uniform and finely divideddispersion of the optional metallic components. The reduction may beeffected in the process equipment of the aromatic complex. Substantiallypure and dry hydrogen (i.e., less than about 100 vol. ppm, preferablyabout 20 vol. ppm, H₂O) preferably is used as the reducing agent. Thereducing agent can contact the catalyst at conditions, including atemperature of about 200-about 650° C. and a period of about 0.5-about10 hours, effective to reduce substantially all of the Group VIII metalcomponent to the metallic state. In some cases, the resulting reducedcatalyst may also be beneficially subjected to presulfiding by a knownmethod such as with neat H₂S at room temperature to incorporate in thecatalyst an amount of about 0.05-about 1.0%, by weight, sulfur,calculated on an elemental basis.

The elemental analysis of the components of the zeolite and/or catalyst,such as noble metal component and/or the at least one alkali metal canbe determined by Inductively Coupled Plasma (ICP) analysis according toUOP Method 961-98. The elemental analysis of an alkali metal, such assodium, in an alumina binder, such as V-251 binder, can be conducted byICP or atomic adsorption spectroscopy analysis. Regarding atomicadsorption spectroscopy analysis, sodium content can be determinedaccording to UOP Method 410-85 and potassium content can be determinedaccording to UOP Method 878-87.

Generally, catalysts described herein have several beneficial propertiesthat provide isomerization of ethylbenzene while minimizing C8ring-loss. Although not wanting to be bound by theory, it is generallythought that the higher levels (greater than about 100 ppm, by weight,calculated on an elemental basis based on the weight of the catalyst) ofat least one alkali metal can reduce C8 ring loss. Thus, contacting anon-equilibrium C8 aromatic feed with an extruded C8 alkylaromaticisomerization catalyst can provide an isomerized product with a C8 ringloss of no more than about 2.5, about 2.0-about 2.5, or about 2.5.

In addition, a catalyst described herein generally has a piece densityof less than about 1.250 g/cc, preferably of less than about 0.950 g/cc,more preferably of less than about 0.900 g/cc, and optimally about0.800-about 0.890 g/cc as determined by mercury displacement accordingto UOP-766-91. Furthermore, the catalyst described herein generally hasa surface area (may be referred herein as BET-SA) of at least about 190m²/g, preferably at least about 210 m²/g, and optimally about 220-about250 m²/g as determined by UOP-874-88. All the UOP methods, such as UOP410-85, UOP-766-91, UOP-874-88, UOP 878-87 and UOP-961-98, discussedherein can be obtained through ASTM International, 100 Barr HarborDrive, West Conshohocken, Pa., USA.

Illustrative Embodiments

The following examples are intended to further illustrate the subjectcatalyst. These illustrations of embodiments of the invention are notmeant to limit the claims of this invention to the particular details ofthese examples. These examples are based on engineering calculations andactual operating experience with similar processes.

The exemplary catalysts can have a commercially synthesized MTW zeoliteand an alumina source of either VERSAL-251 sold by UOP, LLC, an aluminasold under the trade designation CATAPAL C by Sasol North America ofHouston, Tex., or an aluminum hydroxychloride hydrosol (alsol or ODSalumina). All of these alumina sources can be converted to gamma aluminaby heat treatment, yet they have different properties and performance.Although the VERSAL-251 (V-251) and CATAPAL C, which are both boehmitealuminas normally used to prepare extrudates, and the alsol is normallyused to prepare oil dropped spheres, generally the ultimate catalystshape is not determined by the alumina source. Spherical catalysts canbe prepared from boehmite alumina binders and oil dropped spheres may beformed into extrudates.

To form the extrudate supports, the alumina is usually at leastpartially peptized with a peptizing agent such as nitric acid. Thezeolite can be mixed with the at least partially peptized alumina or maybe mixed with the alumina prior to peptization. Afterwards, typicallythe alumina and MTW zeolite mixture is extruded into a cylinder or atri-lobe shape. That being done, the extrudate can be dried and thencalcined at about 540-about 650° C. for about 60-about 90 minutes.

The catalysts can be washed with ammonium nitrate or ammonium hydroxide,or not washed. If washed, the catalyst may be washed at a temperature of90° C. for 5 hours. For an ammonium nitrate solution, the solution caninclude 1 g of ammonium nitrate and 5.7 g of water per gram of catalyst.For an ammonium hydroxide solution, 0.5%, by weight, of NH₃, in watercan be used. The washing step may be conducted on the formed andcalcined support prior to addition of the noble metal.

To form the oil-dropped support, an MTW zeolite is mixed with alsol.Generally, the alsol and MTW zeolite mixture is mixed with a gellingagent of hexamethylene tetraamine. Afterwards, the spheres can be formedand aged in the oil-dropping process. Next, the ODS supports may bewashed with about 0.5% ammonia, and calcined at about 540-about 650° C.for about 90 minutes.

The following can be undertaken for both the extruded supports and theODS supports. Namely, all the supports can be impregnated with platinumwith a solution of chloro-platinic acid mixed with water and HCl.Generally, the HCl is in an amount of 2%, by weight, of the support, andthe excess solution is evaporated.

Next, the supports can be oxidized or calcined at a temperature of about565° C. for about 60-about 120 minutes in an atmosphere of about 5-about15 mol % of steam with a water to chloride ratio of about 50:1-about120:1.

Generally afterwards, the supports are reduced at about 565° C. forabout 120 minutes in a mixture of at least about 15 mol % hydrogen innitrogen. That being done, the supports can be sulfided in a 10 mol %atmosphere of hydrogen sulfide in a hydrogen sulfide and hydrogenmixture at ambient conditions to obtain about 0.07%, by weight, sulfuron the support to obtain the final catalysts. A depiction of thematerials and methods for forming the exemplary catalysts is provided inthe table below:

TABLE 1 Catalyst Amount Example Support Forming Alumina MTW No. TypeShape Method Source Weight % Wash A1 IX'd CB Trilobe Extrusion V-251 5NH₄OH A2 CB Trilobe Extrusion V-251 5 None A3 IX'd CB Trilobe ExtrusionV-251 5 NH₄NO₃ A4 IX'd CB Cylindrical Extrusion V-251 5 NH₄NO₃ A5 CBTrilobe Extrusion V-251 10 None A6 CB Trilobe Extrusion V-251 10 None A7IX'd CB Trilobe Extrusion V-251 10 NH₄NO₃ A8 IX'd CB Trilobe ExtrusionV-251 10 NH₄OH A9 CB Trilobe Extrusion V-251 5 None B1 CB Sphere OilDropping ODS 5 NH₄OH B2 CB Sphere Oil Dropping ODS 5 NH₄OH B3 IX'd CBCylinder Extrusion ODS 5 NH₄NO₃ C1 IX'd CB Cylinder Extrusion Catapal C5 NH₄NO₃ C2 IX'd CB Cylinder Extrusion Catapal C 5 NH₄OHAs used in the table, the term “CB” refers to a calcined base includingthe binder and zeolite, and the term “IX'd CB” refers to a calcined basewashed with a solution of NH₄OH or NH₄NO₃, as depicted in the “Wash”column for that row in TABLE 1.

The following data are depicted for the reduced catalysts in thefollowing table. The LOI is conducted in accordance with UOP-275-98. Allcomponents are provided in percent, by weight.

TABLE 2 Catalyst LOI Cl Pt Si Na K Example @ 900° C. Weight WeightWeight Weight Weight No. Weight % % % % % % A1 1.45 0.61 0.326 2.240.021 0.015 A2 0.86 0.74 0.458 2.25 0.022 0.015 A3 0.34 0.58 0.314 2.280.003 <0.005 A4 0.95 0.61 0.309 2.26 0.003 <0.005 A5 0.10 0.62 0.3133.55 0.030 0.025 A6 0.70 0.65 0.450 3.55 0.031 0.025 A7 0.53 0.58 0.3163.58 0.004 <0.005 A8 0.47 0.59 0.315 3.62 0.025 0.021 A9 0.60 0.04 0.3102.27 0.036 0.031 B1 1.14 0.49 0.311 2.45 0.008 <0.005 B2 1.45 0.63 0.3002.28 0.009 <0.005 B3 1.40 0.57 0.324 2.10 <0.002 <0.005 C1 1.00 0.670.320 2.24 <0.002 <0.005 C2 0.58 0.61 0.308 2.24 0.014 0.012

Moreover, the reduced catalysts are evaluated for several propertymeasurements, as depicted below:

TABLE 3 Piece Density % Pore Volume Catalyst (Volatile Free) BET-SAGreater Than Example No. g/cc square-meter/gram 100 Å % A1 0.868 230 81A2 0.869 247 72 A3 0.869 223 83 A4 0.839 226 83 A5 0.874 242 81 A6 0.872239 81 A7 0.886 237 81 A8 0.879 242 80 A9 0.867 223 83 B1 0.924 208 86B2 0.969 208 — B3 0.909 193 88 C1 1.209 216 61 C2 1.203 207 65

The amount of sodium and potassium in the MTW zeolite and the amount ofsodium in the binder in the reduced catalysts before sulfiding aredepicted below:

TABLE 4 Catalyst MTW Na MTW K Alumina Alumina Na Example No. Weight %Weight % Source Weight % A1 0.224 0.265 V-251 0.0079 A2 0.224 0.265V-251 0.0079 A3 0.224 0.265 V-251 0.0079 A4 0.224 0.265 V-251 0.0079 A50.224 0.265 V-251 0.0079 A6 0.224 0.265 V-251 0.0079 A7 0.224 0.265V-251 0.0079 A8 0.224 0.265 V-251 0.0079 A9 0.564 0.555 V-251 0.0079 B10.224 0.265 ODS — B2 0.224 0.265 ODS — B3 0.224 0.265 ODS — C1 0.2240.265 Catapal C N/A C2 0.224 0.265 Catapal C N/A

Most of the catalysts from Table 2 are sulfided and evaluated for C8aromatic ring loss using a pilot plant flow reactor processing anon-equilibrium C8 aromatic feed having the following approximatecomposition in percent, by weight:

TABLE 5 Feed Composition Component Weight % Ethylbenzene 14 Para-xylene<1 Meta-xylene 55 Ortho-xylene 22 Toluene 1 C8 Paraffins <1 C8Naphthenes 6 Water 100-200 ppm

This feed is contacted with a catalyst at a pressure of about 700kPa(g), a weight hourly space velocity (may be referred to as WHSV) of8.0 hr⁻¹, and a hydrogen/hydrocarbon mole ratio of 4. The reactortemperature is about 385° C.

The “C8 ring loss” is in mole percent as defined as “(1-(C8 naphthenesand aromatics in product)/(C8 naphthenes and aromatics in feed))*100”,which represents a loss of one or more C8 rings that can be convertedinto a desired C8 aromatic, such as paraxylene. This loss of feedgenerally requires more feed to be provided to generate a given amountof product, reducing the profitability of the unit. Generally, a lowamount of C8 ring loss is a favorable feature for a catalyst. The “C8ring loss” (may be abbreviated herein as “C8RL”) can be measured in thetable below at conversion of the following formula:

pX/X*100%=22.2±0.05%

where:

-   pX represents moles of para-xylene in the product; and-   X represents moles of xylene in the product.

Generally, the WHSV is set at 8 hr⁻¹ at the start of the test and isincreased until pX/X*100%=22.2±0.05%. Exemplary catalysts are tested inthe pilot plant for C8 ring loss with the following results:

TABLE 6 Catalyst Na + K C8RL Example No. PPM Mole % WHSV A1 360 2.1 9.7A2 370 2.1 11.0 A3 <80 2.4 11.5 A4 <80 2.6 9.7 A5 550 2.3 17.0 A6 5602.3 17.0 A7 <90 3.0 18.0 A8 460 2.4 15.0 A9 670 2.0 6.4 B1 <130 2.6 10.7B3 <70 3.0 12.0 C1 <70 3.4 10.2 C2 260 2.6 9.7

As depicted above, the C8 ring loss is compared with the total alkalimetal content at a given WHSV. Catalysts having more than about 200 ppmof sodium and potassium and derived from VERSAL-251 alumina have C8RLvalues ranging from 2.0-2.4 mole percent with an average C8RL of 2.2mole percent. These values are substantially lower than the C8RL valuesfor either catalysts derived from CATAPAL C alumina (ranging from2.6-3.4 mole percent and averaging 3.0 mole percent) or an ODS alumina(ranging from 2.6-3.0 mole percent and averaging 2.8 mole percent).

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing, all temperatures are set forth uncorrected in degreesCelsius and, all parts and percentages are by weight, unless otherwiseindicated.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A process for isomerizing a non-equilibrium C8 aromatic feed toprovide an isomerized product, comprising: A) contacting thenon-equilibrium C8 aromatic feed with an extruded C8 alkylaromaticisomerization catalyst, wherein the extruded catalyst comprises: 1)about 2-about 20%, by weight, of an MTW zeolite; 2) about 80-about 98%,by weight, of a binder comprising an alumina; 3) about 0.01-about 2.00%,by weight, of a noble group metal calculated on an elemental basis; and4) about 100 ppm-less than about 1000 ppm, by weight, of at least onealkali metal calculated on an elemental basis; wherein the weightpercents of the MTW zeolite, the binder, the noble group metal, and atleast one alkali metal are based on a weight of the extruded catalyst;and B) providing the isomerized product having a C8 ring loss of no morethan about 2.5.
 2. The process according to claim 1, wherein theisomerized product has a C8 ring loss of about 2.0-about 2.5.
 3. Theprocess according to claim 1, wherein the at least one alkali metalcomprises sodium and the extruded catalyst comprises at least about 150ppm, by weight, of sodium calculated on an elemental basis based on theweight of the extruded catalyst.
 4. The process according to claim 1,wherein the at least one alkali metal comprises potassium and theextruded catalyst comprises at least about 50 ppm, by weight, ofpotassium calculated on an elemental basis based on the weight of theextruded catalyst.
 5. The process according to claim 1, wherein theextruded catalyst comprises: about 5-about 10%, by weight, of the MTWzeolite; and about 90-about 95%, by weight, of the binder; wherein theweight percents of the MTW zeolite and the binder are based on theweight of the extruded catalyst.